1. Field of the Invention
The present invention relates to a pin-feed apparatus for carrying a sheet with perforations through a recording system such as printer, facsimile or typewriter.
2. Related Background Art
A sheet carrier mechanism for recording systems may use a pin-feed apparatus for carrying a sheet (recording medium such as a sheet of paper, plastic or the like) in a stable manner. The pin-feed apparatus includes pin-shaped means adapted to cooperate with perforations on the opposite side edges of a continuous sheet such as a fan-folded sheet or the like.
Such a pin-feed apparatus is of either a pin-wheel type or a pin-tractor type. Usually, pin-wheels or pin-tractors are disposed one on each side of the path of sheet movement. The pin-wheels or pin-tractors are rotatably supported on a pin-feed body and driven by a pin-feed shaft which may serve also as a platen drive shaft.
The arrangement of such a pin-feed apparatus may be of a coaxial type in which the pin-feed apparatus is disposed coaxially on a platen roller (sheet carrying roller), a press-in type in which the pin-feed apparatus is located in front of the recording station or a pull-out type in which the pin-feed apparatus is positioned at the outlet of the recording station.
The pin-feed apparatus must handle different widths of sheets and may have such a construction that the spacing between the pin-wheels or pin-tractors can be adjusted.
However, the prior art pin-feed apparatus having the above construction comprises a guide shaft extending parallel to the pin-feed shaft and a locking lever for locking the pin-feed body after the position thereof has been confirmed by observing matching marks. This raises problems in that the positioning operation is troublesome and in that the construction is complicated with an increased number of components resulting in increase of cost in manufacturing.
Japanese Utility Model Application 494/1982 (Laid Open 104658/1983), assigned to the assignee, discloses a construction of the pin-feed apparatus which intends to simplify the positioning operation and to reduce the cost in manufacturing. Such a construction comprises a shaft guiding the pin-tractors and including grooves formed thereon in place and ball means located on the pin-tractors and urged against the shaft under the action of spring means, whereby the ball means can engage into the grooves to position the pin-tractors in place in a click manner. However, this construction of the pin-feed apparatus also has a disadvantage in that jamming of the sheet is easily created if the spacing between the lines of perforations on the sheet has an accidental error or if there is any change in the width of the sheet due to change of the circumstance around the pin-feed apparatus.